RHYTHMICAL PULSATION IN ANIMALS. 



1. PULSATION OF JELLYFISHES, ARMS OF LEPAS, HEART OF 

 SALPA AND OF LOGGERHEAD TURTLE. 



I. CONCLUSIONS NEW TO SCIENCE. 



1. If we cut off the marginal sense-organs of the scyphomedusa 

 Cassiopea, the disk* becomes paralyzed and does not pulsate in sea- 

 water. The disk will pulsate in sea-water, however, if we make either 

 a single ring or a series of concentric broken-ring-like cuts through 

 the muscular tissue of the sub-umbrella. Then upon momentarily 

 stimulating the disk in any manner, it suddenly springs into rapid, 

 rhythmical pulsation so regular and sustained as to recall the move- 

 ment of clockwork. 



Pulsation will not start unless the disk be momentarily stimulated, 

 as by a mechanical or electrical shock or by a single touch with a 

 crystal of K 2 SO 4 , but once started it continues indefinitely in normal 

 sea- water without further external stimulation. 



The waves of pulsation all arise from the stimulated point, and the 

 labyrinth of sub-umbrella tissue around this center must form a closed 

 circuit . It is not necessary that the cuts through the sub-umbrella tissue 

 of the disk be concentric circles, for any shape will pulsate which 

 allows contraction waves to travel through tissue forming a closed cir- 

 cuit from the stimulated center and back to this center. When each 

 wave returns to the center it is reinforced and again sent out through 

 the circuit; and thus the center sustains the pulsation. 



NOTE. It is a pleasure to express my gratitude to those who have aided me in the 

 prosecution of this research. To Prof. H. S. Jennings for his kindness in sending to 

 me lists of the coefficient i for the making of isotonic solutions ; to Dr. Leon J. 

 Cole and Dr. Charles Zeleny for important suggestions and criticisms; to Mr. Daven- 

 port Hooker for collecting Gonionemus and Dactylometra, and to Prof. H. F. Perkins 

 for aid in collecting Cassioj>ea at Tortugas ; to Professors Ulrich Dahlgren and Edward 

 L. Mark for instruction and aid. 



*In this paper the term "disk" will be used to designate Medusae from which the 

 marginal sense-organs have been excised ; while the term ' ' Medusa ' ' will designate the 

 normal perfect animal. 



